ABERDEEN, UNITED KINGDOM (AFP) - Scottish First Minister Nicola Sturgeon was set to ramp up the rhetoric in her demands for another secession referendum when she rallies her independence-hungry foot soldiers on Saturday (March 18).

Sturgeon was to address a conference of her Scottish National Party (SNP) in the north-eastern oil city of Aberdeen, with members fired up by her push for a second vote on pulling Scotland out of the United Kingdom.

Sturgeon caught the British government off-guard on Monday when she demanded a new referendum by early 2019 at the latest, just before Britain is expected to leave the European Union.

In response, British Prime Minister Theresa May said "now is not the time" for another referendum, arguing all energies should be devoted to getting a good Brexit deal for Britain as a whole.

That has outraged the SNP.

Sturgeon on Wednesday is set to obtain the Scottish Parliament's authority for her to ask the British government for the powers to hold a legally-binding referendum.

In Scotland's 2014 plebiscite, 55 per cent backed staying in Britain. But the SNP says the political landscape has dramatically changed since then.

It argues the vote was based on expectations that Britain would remain in the EU, retaining its unhampered access to the European market and the right of job mobility.

These rights could be swept away if May, after last June's Brexit referendum, brutally severs ties with the EU, the SNP says.

Sturgeon, in remarks trailed ahead of delivery, will warn of the consequences of ignoring the clamour for a second referendum.

"To stand in defiance... would be for the prime minister to shatter beyond repair any notion of the UK as a respectful partnership of equals," Sturgeon was expected to say.

"Whatever our different opinions on independence, we can all unite around this simple principle - Scotland's future must be Scotland's choice."

On Friday, May, speaking to her centre-right Conservative Party, said the SNP were stuck in the "tunnel vision" of "obsessive nationalism".

"It is now clear that using Brexit as the pretext to engineer a second independence referendum has been the SNP's sole objective," she said.

In the 2016 EU membership referendum, 62 per cent of voters in Scotland wanted Britain to remain in the bloc.

But 52 per cent backed Brexit across the whole of Britain - a figure driven by voting in England, with which Scotland has an often fraught history.

On the back of the Brexit vote, Sturgeon now wants another referendum between late 2018 and early 2019, before Britain leaves the EU.

The Scottish government's Brexit minister, Mike Russell, told AFP that May was saying, "It doesn't matter what you think', it's only what she thinks.

"That is not democratically acceptable. It is, as the first minister has said, an outrage."

SCOTLAND WILL HAVE ITS REFERENDUM

Sturgeon also let it be known that she would be "up for continued discussion" with May regarding the timing of a referendum, but it would be unacceptable for the vote to be denied.

Scotland's relationship with the EU is at the forefront of the SNP's renewed call for independence.

For SNP MP Christian Allard, a Frenchman and Scottish resident for 30 years: "The SNP's policy is to be in the EU, but if there are any difficulties or if there is a transition period, we are quite happy to be in the single market." But the SNP is also banking on a growing desire for independence.

According to the latest annual ScotCen Scottish Social Attitudes survey released on Wednesday, 46 per cent of Scottish voters now back breaking away from Britain.

This is the highest level of support for independence since the survey started in 1999.

In 2012, as the SNP's former leader Alex Salmond highlighted, that figure stood at 20 per cent.

For this reason, he added, the party has every reason to be confident.